I need some direction, please. 2011 DF90 with 275 hours which was running flawlessly until recently. The last three trips out now include the RPM varying seemingly a couple hundred RPM. I don't hear it until I get it in the range of 2000 - 5500 RPM. It may happen below 2000 or above 5500 RPM, but I can't detect it. I can't ever feel it (as a surge), but can hear it and do see it on a Simrad digital display. Cannot see it on an analog gauge. Motor doesn't really run rough, but as if I am moving the throttle deliberately slower and then back every 1/2 second or so. I have held the throttle lever steady, so it's not that it is actually loose. I did not think about running it up to 2000+ out of gear.
If we go at least a few miles across the lake the past three trips (different distances each time), the varying RPM goes on continuously until we get to our spot and stop for a couple of hours. The return trip is back to flawless - RPM is steady. We have ran on for many more miles on the return trip without any issues. The only thing recently was a refuel from a marina with labelled non-ethanol gas which I have used in past years without issues. Past history may not matter, though. I added a heavy dose of fuel additive yesterday before this third trip, but did not have the chance to run it today.
I replaced plugs, fuel filter on motor and inline fuel/water separator filter at about 250 hours. Water separator window is clean. I don't find any gauge warning indicators on. Oil level indicates at the upper end of the stick's range. Water temps run approximately 138 degrees. Pee stream is normal. Running voltage is just under 14 volts and alternator is right at 15 volts both per Simrad display. Normally cruise at 4K RPM.
What could this possibly be? Thanks!
If we go at least a few miles across the lake the past three trips (different distances each time), the varying RPM goes on continuously until we get to our spot and stop for a couple of hours. The return trip is back to flawless - RPM is steady. We have ran on for many more miles on the return trip without any issues. The only thing recently was a refuel from a marina with labelled non-ethanol gas which I have used in past years without issues. Past history may not matter, though. I added a heavy dose of fuel additive yesterday before this third trip, but did not have the chance to run it today.
I replaced plugs, fuel filter on motor and inline fuel/water separator filter at about 250 hours. Water separator window is clean. I don't find any gauge warning indicators on. Oil level indicates at the upper end of the stick's range. Water temps run approximately 138 degrees. Pee stream is normal. Running voltage is just under 14 volts and alternator is right at 15 volts both per Simrad display. Normally cruise at 4K RPM.
What could this possibly be? Thanks!
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